Maintaining RAASi Treatment with Optimal Potassium Control

Inclusion Criteria:

* Patients must present serum potassium levels of 5.5-6.5 mEq/L at patient selection visit (V0)
* Patients must present serum potassium levels of 5.0-6.5 mEq/L at randomization visit (V1).
* Provision of patient or legal representative informed consent prior to any study specific procedures.
* Individuals receiving background standard of care for HF and treated according to locally recognized guidelines. Specific treatment should include RAASi and/or MRA treatment at first consultation and at least should have been stable for ≥ 4 weeks at maximum tolerated doses.
* Patients with CKD not on dialysis (Stages 2-5: estimated glomerular filtration rate (eGFR) between 15-60 ml/min/1,73m2 or eGFR between 60-90 ml/min/ 1.73 m2 with albuminuria/creatinuria (\> 30 mg/g) in the previous three months). The estimated GFR can be reported by the laboratory or calculated by the researcher with serum creatinine, age, and sex (CKD-EPI equation).
* 18 years at the time of signing ICF.
* Negative pregnancy test (urine or serum) for female subjects of childbearing potential.
* Female subjects must be 1 year post-menopausal, surgically sterile, or using an acceptable method of contraception (an acceptable method of contraception is defined as a barrier method in conjunction with a spermicide) for the duration of the study (from the time they sign ICF) and for 3 months after the last dose of SZC. In addition, oral contraceptives, approved contraceptive implant, long-term injectable contraception, intrauterine device, or tubal ligation are allowed. Oral contraception alone is not acceptable; additional barrier methods in conjunction with spermicide must be used.

Exclusion Criteria:

* Involvement in the planning and/or conduct of the study (applies to both Investigator staff and/or staff at the study site).
* Previous enrollment or randomization in the present study.
* HF due to restrictive cardiomyopathy, active myocarditis, constrictive pericarditis, hypertrophic (obstructive) cardiomyopathy or uncorrected primary valvular disease.
* Current acute decompensated HF, hospitalization due to decompensated HF, myocardial infarction, unstable angina, stroke or transient ischemic attack within 12 weeks prior to enrollment.
* Coronary revascularization (percutaneous coronary intervention or coronary artery bypass grafting or valvular repair/replacement within 12 weeks prior to enrollment or planned to undergo any of these operations after randomization).
* Implantation of a Cardiac Resynchronization Therapy (CRT) device or Implantable Cardioverter Defibrillator (ICD) within 12 weeks prior to enrollment or intent to perform atrial fibrillation ablation or to implant a CRT or ICD device.
* Previous cardiac transplantation or implantation of a ventricular assistance device or similar device, or transplantation or implantation expected after randomization
* Oropharingeal dysfunction that precludes normal swallow.
* Female who is pregnant, breast-feeding or intends to become pregnant or is of child-bearing potential and not using a highly effective contraceptive method.
* Patients with amputated limbs or pacemaker devices will be excluded of bioimpedance analysis.
* Participation in another clinical study with an investigational product during the last 6 months.
* Patients with a known hypersensitivity to SZC or any of the excipients of the product.
* Treated with potassium binding resins such as sodium polystyrene sulfonate (SPS; e.g. Kayexalate®) or calcium polystyrene sulfonate (CPS; e.g. Resonium®) or the cation exchange polymer, patiromer sorbitex calcium (Veltassa®), within 7 days prior to the first dose of study drug.
* Judgment by the investigator that the subject should not participate in the study if the subject is unlikely to comply with study procedures, restrictions and requirements.
* Subjects with a family history of long QT syndrome, presence of cardiac arrhythmias or conduction defects that require immediate treatment, or a QTc (corrected QT interval) of ≥ 550 msec.
* History of QT prolongation associated with other medications that required discontinuation of that medications.
* Symptomatic or uncontrolled atrial fibrillation despite treatment, or asymptomatic sustained ventricular tachycardia. Subjects with atrial fibrillation controlled by medication are permitted.